The present invention relates generally to systems for managing charge flow and EGR fraction in an EGR control system for an internal combustion engine, and more specifically to such systems for controllably arbitrating between commanded values of charge flow and EGR fraction and the physical capabilities of corresponding EGR and/or turbocharger control mechanisms.
Systems for controlling EGR flow and/or turbocharger swallowing capacity are known and have been widely implemented, particularly in the heavy diesel engine industry. An example of one known system 10 for providing such control is shown in FIG. 1 and includes an internal combustion engine 12 having an intake manifold 14 fluidly coupled to a compressor 18 of a turbocharger 25 via intake conduit 16, wherein the compressor 18 receives fresh air via intake conduit 20. The turbocharger compressor 18 is mechanically coupled to a turbocharger turbine 24 via drive shaft 22, wherein turbine 24 is fluidly coupled to an exhaust manifold 28 of engine 12 via exhaust conduit 30, and is further fluidly coupled to ambient via exhaust conduit 26. An EGR valve 32 is disposed in fluid communication with the intake conduit 16 and the exhaust conduit 30, and a differential pressure sensor, or xcex94P sensor, 34 is disposed across the EGR valve 32 to sense a pressure change, or delta pressure, across valve 32. An electronic EGR flow controller 36 has a first input receiving a signal indicative of desired EGR valve position, and has a first output electrically connected to EGR valve 32 via signal path 38. In the system shown in FIG. 1, the EGR flow controller is configured to apply the EGR position signal directly to the EGR valve 32. Controller 36 includes a second input receiving a signal indicative of a desired delta pressure value, or xcex94P target, and a third input electrically connected to the xcex94P sensor 34 via signal path 40 and receiving a signal thereat indicative of sensed delta pressure (xcex94P). The xcex94P value is subtracted from the xcex94P target value within the EGR flow controller 36 and a xcex94P error value produced thereby is applied to a proportional-integral (PI) or other known controller 44. An output of controller 44 produces a variable geometry turbocharger signal VGT that is used to control the swallowing capacity and/or efficiency of the turbocharger 25 via any of a number of known techniques via signal path 46. In operation, charge flow to the engine 12, defined for the purposes of the present invention as the sum of fresh air flow into intake conduit 16 and EGR flow into intake conduit 16, is controlled via control of the position of the EGR valve 32 and the pressure differential between the exhaust conduit 30 and intake conduit 16.
One drawback associated with an EGR flow control system 10 of the type illustrated in FIG. 1 is that there exists an interdependency between charge flow and EGR flow such that EGR flow and fresh air flow cannot be controlled separately. Once EGR flow is established by the EGR flow controller 36, the resulting charge flow is defined by whatever fresh air flow is available. System 10 may therefore be optimized for NOx control or for particulate control, but generally not for both. It is accordingly desirable to provide for an EGR control system wherein EGR flow and fresh air flow may be controlled separately to therefore gain better and more consistent control over the charge flow. Such a system for achieving this goal is described in co-pending U.S. patent application Ser. No. 09/773,654, entitled SYSTEM FOR DECOUPLING EGR FLOW AND TURBOCHARGER SWALLOWING CAPACITY/EFFICIENCY CONTROL MECHANISMS, which is assigned to the assignee of the present invention and the contents of which are incorporated herein by reference.
In such a system, however, it is further desirable to provide a control strategy that arbitrates between EGR/turbocharger control commands and the corresponding capabilities of the EGR and/or turbocharger control mechanisms. In conventional EGR/turbocharger control systems, EGR/turbocharger control commands are typically( based on open-loop control techniques, and therefore do not take into account current operating states of the various EGR system and/or turbocharger actuators. As a result, the desired EGR/turbocharger control commands may request one or more of the various EGR system and/or turbocharger actuators to respond in a manner that, due to its current operational state, it cannot satisfy or should not satisfy due to potential violation of a related operational constraint. What is therefore needed is a control strategy that limits EGR/turbocharger control commands based on current EGR system and/or turbocharger operating conditions and/or based on the capabilities of the EGR system and/or turbocharger control mechanisms.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for managing charge flow and EGR fraction in an internal combustion engine comprises a valve disposed between an exhaust manifold and an intake manifold of an internal combustion engine, means for determining a differential pressure across the valve resulting from flow of exhaust gas from the exhaust manifold to the intake manifold, a valve position sensor producing a position signal indicative of a position of the valve relative to a reference valve position, and a control circuit limiting a commanded EGR fraction value to a limited EGR fraction value as a function of the differential pressure signal and of the position signal.
In accordance with another aspect of the present invention, a system for managing charge flow and EGR fraction in an internal combustion engine comprises a turbocharger for an internal combustion engine including a compressor supplying fresh air to an intake manifold of the engine, means for determining an outlet temperature of the compressor, a limiter producing a penalty value as a function of the outlet temperature, and a control circuit limiting a commanded charge flow value to a limited charge flow value as a function of the penalty value.
In accordance with yet another aspect of the present invention, a system for managing charge flow and EGR fraction in an internal combustion engine comprises a turbocharger for an internal combustion engine including a compressor supplying fresh air to an intake manifold of the engine, a speed sensor producing a speed signal indicative of a rotational speed of the compressor, a limiter producing a penalty value as a function of the speed signal, and a control circuit limiting a commanded charge flow value to a limited charge flow value as a function of the penalty value.
In accordance with still another aspect of the present invention, a system for managing charge flow and EGR fraction in an internal combustion engine comprises a valve disposed between an exhaust manifold and an intake manifold of an internal combustion engine, means for determining a differential pressure across the valve resulting from flow of exhaust gas from the exhaust manifold to the intake manifold, a limiter producing a penalty value as a function of the differential pressure, and a control circuit limiting a commanded charge flow value to a limited charge flow value as a function of the penalty value.
In accordance with a further aspect of the present invention, a system for managing charge flow and EGR fraction in an internal combustion engine comprises a turbocharger for an internal combustion engine including a compressor supplying fresh air to an intake manifold of the engine, means for determining an outlet temperature of the compressor, a speed sensor producing a speed signal indicative of a rotational speed of the compressor, a first limiter producing a first penalty value as a function of the outlet temperature, a second limiter producing a second penalty value as a function of the speed signal, and a control circuit limiting a commanded charge flow value to a limited charge flow value as a function of at least one of the first and second penalty values. The system may further include a valve disposed between an exhaust manifold and the intake manifold of the engine, means for determining a differential pressure across the valve resulting from flow of exhaust gas from the exhaust manifold to the intake manifold, and a third limiter producing a third penalty value as a function of the differential pressure, and wherein the control circuit is operable to limit the commanded charge flow value to the limited charge flow value as a function of at least one of the first, second and third penalty values.
One object of the present invention is to arbitrate between desired EGR system and/or turbocharger behavior and the actual capabilities of EGR system and/or turbocharger control mechanisms under current operating conditions.
Another object of the present invention is to provide a system for managing EGR fraction in an internal combustion engine by limiting an EGR fraction command as a function of current engine operating conditions.
Yet another object of the present invention is to provide a system for managing charge flow in an internal combustion engine by limiting a charge flow command as a function of current engine operating conditions.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.